In recent years broadband services like broadcast TV, video on demand (VoD) or mobile Internet play an increasingly important role. In order to obtain a lower cost-per-bit-effective transport of the signals to be transported, a new generation packet network technology has been developed, which requires new methods for transferring time information. It shall be noted that, throughout this description, the term “time information” refers to information concerning the absolute or relative time and information concerning frequency and phase of a timing signal. Many of these new time information transfer methods are not at the physical layer, but involve the network and data link layers and are thus affected by the packet network behavior. In order to characterize the packet network behavior, suitable instrumentation and analysis techniques for characterizing packet latency and packet delay variation have been developed.
Packet synchronization services have been evolving services during the last few years, fueled by massive rollout of advanced mobile networks.
A widely used possibility for distributing timing information over a packet-based network is the synchronous Ethernet protocol (syncE) which provides synchronization (frequency synchronization) on the physical ethernet layer.
Additionally, other protocols for transferring precision time information over a packet network on higher layers have been developed, among others, the Network Time Protocol (NTP) and Precision Time Protocol (PTP) as defined in IEEE 1588v2. Systems for realizing high-performance time information transfer using these protocols include components for precision packet timing measurements, especially a common precision primary clock reference from a source (such as a PTP master clock) and hardware having timestamping capability. Such equipment has been developed over the last several years and makes it possible to perform packet delay measurements in the laboratory and in operating networks.
A plurality of metrics have been proposed for assessing the stability and quality of packet based time information. Especially, the Time Interval Error (TIE), Maximum Time Interval Error (MTIE), Minimum Time Deviation (minTDEV), Maximum Average Time Interval Error (MATIE) and Maximum Average Frequency Error (MAFE) are, among others, useful metrics to assess the stability and quality of packet-based time and frequency information. Like all metrics proposed for packet synchronization services assessment, these metrics imply the measurement of recovered clock performance data or specific transport attributes of the packet network and the comparison of the results obtained with predefined target performance masks.
The interpretation and analysis of such packet timing data still is a rather challenging task as a certain level of knowledge and understanding of the measurement results is required. Further, a precise synchronization reference is required for the measurements, which is not always available at the network node at which the synchronization service quality is to be assessed. Lastly, these methods are more suitable for the synchronization services diagnostics and less fit performance monitoring needs.
For assessing the quality of a given service, the use of scores is known in a variety of technical fields. For example, the mean opinion score (MOS) is used in telephony networks. MOS is specified by ITU-T P.800 “Methods for subjective determination of transmission quality”. Further, US 2004/0151127 A1 discloses a method and a system for calculating both transmission impairment test (TIT) scores and quality of service (QoS) scores for signal transmissions over a communications network.